This error can be seen when working with regular expressions and character lists.
ORA-12728: invalid range in regular expressionFor a live simulation of this error, see Yocoya's Regular Expression Workbench.
While in this case it's easy to see that the character range is incorrect because letter c precedes letter a, whereas it should be written as [a-c], it can be harder to understand when multicharacter elements are present:
for instance, range [a-[.ch.]] is legitimate when NLS_SORT is set to XSPANISH, however range [[.ch.]-[.ll.]] is not.
For further details about NLS_SORT settings, see a previous posting.
Note also that you can put multiple character ranges inside lists as in [0-9a-z], however accented characters will not match.
If you need to include normal letters as well as their accented counterparts, use built-in character classes like [[:alnum:]] or [[:alpha:]].
See message translations for ORA-12728 and search additional resources